Hepatitis B virus (HBV) infection is a major public health problem. Over 300,000 new HBV infections and 4,000 deaths occur every year in the United States. A safe and effective vaccine has been available since 1981, and recommendations to vaccinate infants and high risk groups have been in place for the last decade. However, HBV vaccination coverage among adolescent and young adult drug users is low, despite the fact that this population is at high risk for infection. In addition, the difference sin risk for HBV infection among young injectors and non- injectors is not clearly defined. Therefore, I propose to conduct a nested, prospective study to examine and compare the factors involved in HBV infection and HBV vaccine acceptance and completion in young injection drug users (IDUs) and non-injection drug users (NIDUs) in Baltimore, Maryland. The specific aims of the study are as follows: 1) to compare the prevalence and correlates of current and past HBV infection in young adult IDUs and NIDUs; 2) to compare the prevalence and correlates of past HBV vaccination of young adult IDUs and NIDUs; 3) to identify and compare the correlates of acceptance of HBV vaccine among young adult IDUs and NIDUs; and 4) to identify and compare the correlates of completion of the HBV vaccine series among young adult IDUs and NIDUs. By identifying the factors associated with HBV infection and vaccination, the proposed research will provide the critical insight needed to develop tailored interventions to improve HBV vaccination coverage in this high-risk population.